A liquid crystal display (LCD) is a flat display with property of low power consumption, and decreased significantly in either occupied space or weight in comparison with a conventional cathode ray tube (CRT) and without curve surface as a CRT display has. Hence, the liquid crystal display has widely been applied in all sorts of merchandises, including consumptive electronic products, such as pocket calculators, electronic dictionaries, watches, mobile phones, portable notebooks, communication terminals, display panels, desk-top personal computers, and even high dpi (dots per inch) television (HDTV) and so on. The most popular display is an active-type thin film transistor liquid crystal display (TFT-LCD) due to the fact that the viewing angle and the contrast performance are much better than those of a super-twisted nematic liquid crystal display (STN-LCD) of passive matrix type and the TFT-LCD shows more rapid response (such as several tens of milliseconds) than the STN-LCD does (such as several hundred milliseconds).
The primary elements of a TFT-LCD device include a fluorescent light tube, a light-guiding plate, a polarized film, a color filter, two glass substrates, a rubbing film, liquid crystal materials, and thin film transistors. The principle is as follows: At first, a ray is projected from a backlight source, i.e. a fluorescent light tube to a polarized film as well as liquid crystal molecules and cause the ray to changes proceeding direction thereof in accordance with the arrangement of the liquid crystal molecules. Afterward, the light passes through a color filter and another polarized film in order. Then as we vary the voltage actuating the liquid crystal, the intensity and color of the light can be adjusted in accordance with the voltage. Consequently, the liquid crystal panel can then present modes of diverse intensity and colors in response to the data retrieved.
A fluorescent light tube is employed as a backlight source and a diffuser, otherwise at least a side light source and a light-guiding plate are required as an alternative. As a result, more power is consumed and larger space is occupied. To reduce the power consumption and to fabricate a thinner liquid crystal display will be our aim and the reflective type LCD can meet our need. As to the reflective type LCD, since the light primarily comes from outside, the inbuilt lighting device can be simplified such that less space is occupied. Therefore, the reflective LCD can be applied under any environment unless the light is too dim.
Referring to the aforementioned TFT-LCD, in tradition the amorphous silicon has been the primary material in fabricating thin film transistor (TFT). However, for the current polysilicon is used to substitute the amorphous silicon and may become the mainstream in the future. This is because the polysilicon has carrier (either electron or hole) mobility higher than that of the amorphous silicon. Additionally, the polysilicon TFT-LCD has another advantage of being able to form the driving circuit (including nMOS transistor or pMOS transistor and even CMOS transistor) on the LCD panel and the pixels at the same time. As a result of the aforementioned reasons, the polysilicon-type TFT-LCD can be switched at higher speed than the amorphous-type silicon TFT-LCD and thus can catch the most attention. However, the foregoing mentioned polysilicon-type TFT-LCD is restricted to the transparent type TFT-LCD only. The U.S. Pat. No. 5,940,151 invented by Yong-Min Ha is one example.
Therefore, this invention discloses a manufacturing technique for LCD combining the polysilicon type and the reflective type.